A friction agitation joining method belongs to a category of a solid state welding method. The friction agitation joining method has such advantages that it can be applied to various metal joining members regardless of the materials and that joining members are hardly deformed by thermal strains at the time of joining. Thus, in recent years, the method has been used for joining various structural members.
This friction agitation joining method will be explained with reference to FIGS. 29 to 31. In these figures, the reference numeral 101 denotes a long and thin plate-shaped metal first joining member, and 102 denotes a long and thick plate-shaped metal second joining member. These joining members 101 and 102 are butted against each other at the widthwise sides thereof with the lower surfaces being flush with each other (the reference numeral 103 denotes the butted portion). Thus, the level difference corresponding to the thickness difference is formed at the surface side thereof. In this butted state, these joining members 101 and 102 are supported from the lower surface sides thereof by the forward and backward supporting rollers 131 and 132. The reference numeral 104 denotes a stepped portion formed at the surface side of the joining members 101 and 102.
The reference numeral 140 denotes a joining tool for performing a friction agitation joining method. This joining tool 140 is equipped with a columnar rotor 141 having a larger diameter and a pin-shaped probe 142 having a smaller diameter integrally protruded from the rotational center of the end surface of the rotor 141 and extending along the rotation axis Q′.
The reference numeral 133 denotes a backing roller. This backing roller 133 is disposed at the lower surface side of the joining members 101 and 102 opposite to the probe 142 of the joining tool 140.
When joining the butted portion 103 of the joining members 101 and 102 using the friction agitation joining tool 140, first, the rotating probe 142 of the joining tool 140 is inserted into the butted portion 103 of the joining members 101 and 102 from the upper side thereof. Then, in this inserted state, both the joining members 101 and 102 are moved in a longitudinal direction thereof with the probe inserted in the butted portion 103 so that the probe 142 advances along the butted portion 103. “MD′” denotes the moving direction of both the joining members 101 and 102. In accordance with the movement of both the joining members 101 and 102, the butted portion 103 of both the joining members 101 and 102 is joined by the probe 142 at the probe inserted position. The reference numeral 103′ denotes a joined (i.e., welded) butted portion of the joining members 101 and 102. “W′” denotes a joined portion formed at the butted portion 103′. Furthermore, “WD′” shows the joining direction in this friction agitation joining method.
In cases where the joining members 101 and 102 are twisted or curved in the thickness direction, i.e., not formed into a flat shape, joining of such joining members 101 and 102 causes a defect of shape. As a result, high quality joined butted members cannot be obtained. Furthermore, if these joining members 101 and 102 are butted against each other in the state that they have torsion, clearance (not shown) resulting from the torsion of the joining members 101 and 102 will be generated at the butted portion 103. Accordingly, if the butted portion 103 is joined in this state, a joining defect such as a non-joined portion will occur in the joined portion 103′ by the clearance. Furthermore, in cases where the joining members are long or thin members, even if these members are joined by friction agitation joining, thermal distortion due to the joining tends to be produced.
In order to solve this problem, Japanese Unexamined Laid-open Patent Publication No. H10-296462 proposes the following method. In this method, a butted portion will be joined/welded while pressing the joining-direction forward side of both the joining members 101 and 102 with respect to a probe inserted position from the upper surface side thereof by a cylindrical forward pressing roller 110 having a certain length and bridging over both the joining members 101 and 102, and also pressing the joining-direction backward side of both the joining members 101 and 102 with respect to a probe inserted position from the upper surface side thereof by a cylindrical backward pressing roller 110 having a certain length and bridging over both the joining members 101 and 102.
However, since the stepped portion 104 is formed on the surface of the butted portion 103 of the joining members 101 and 102, according to the aforementioned proposed method, even if the forward and backward pressing rollers 110 and 120 are intended to press both the joining members 101 and 102, it was able to press down the thicker joining member 102 with the forward and backward pressing rollers 110 and 120, but was not able to press down the thinner joining member 101. As a result, neither torsion nor curvature could be corrected. Therefore, the joining members 101 and 102 are joined in a state that they have torsion or curvature, and therefore configuration defects, joining defects such as a non-joined state and thermal distortion occur. Accordingly, high quality joined butted members cannot be obtained.
Now, generally, in a friction agitation joining method, it is desirable to execute the joining method in a state in which the probe 142 of the joining tool 140 is deeply inserted into the butted portion 103 so as to join the butted portion 103 in the entire thickness direction thereof.
However, if the friction agitation joining is performed in a state in which the probe 142 is inserted as mentioned above, the tip of the probe 142 may project from the lower surface of the butted portion 103 of the joining members 101 and 102 during the joining process, which in turn may cause a damage to the backing member such as a backing roller 133. In order to prevent such a fault, as shown in FIG. 30, generally the probe 142 is inserted so as to keep the distance between the tip of the probe 142 and the lower surface of the butted portion 103. However, this insufficient insertion of the probe 142 causes insufficient joining of the butted portion 103 with respect to the thickness direction. As a result, as shown in FIG. 31, the root remaining portion R tends to remain in the lower surface of the joined butted portion 103′ where both the joining members 101 and 102 are joined. This root remaining portion R causes reduced bonding strength of the butted joining members.
As shown in FIGS. 30 and 31, especially in cases where both the joining members 101 and 102 are butted against each other with a level difference formed on the surface side in the thickness direction, the root remaining portion R tends to remain. That is, in cases where both the joining members 101 and 102 are butted against each other as mentioned above, it is difficult to stably dispose the end surface 141a of the rotor 141 of the joining tool 140 on both the joining members 101 and 102, and therefore as shown in FIG. 30, the rotor 141 tends to incline to the first joining member side 101 or the second joining member side 102 unexpectedly. Thus, at the time of inclination of the rotor 141, since the insertion depth of the probe 142 in the butted portion 103 changes, it is necessary to reduce the insertion depth of the probe 142 for safety, which in turn tends to generate the root remaining portion R.
Furthermore, as shown in FIG. 30, in this case, since the rotor 141 of the joining tool 140 is usually disposed in a inclined state toward the first joining member side 101, it is difficult to strictly set the insertion depth of the probe 142 into the butted portion 103. Furthermore, since the insertion depth of the probe 142 increases because the shoulder portion 102a of the second joining member 102 deforms plastically during the joining, it is necessary to decrease the insertion depth of the probe 142. For this reason, the root remaining portion R tends to remain.
Furthermore, since the thickness of manufactured joining member 101 and 102 is uneven, it is difficult to keep the constant insertion depth of the probe 142. From this point too, the root remaining portion R tends to remain.
The present invention was made in view of the aforementioned technical background.
It is a first object of the present invention to provide a friction agitation joining method, a method for manufacturing joined butted members and a friction agitation joining apparatus capable of preventing a generation of configuration defects such as twist or curvature and a generation of poor junction such as joint defect or thermal distortion, to thereby provide high quality joined butted members.
It is a second object of the present invention to provide a friction agitation joining method, a method for manufacturing joined butted members and a friction agitation joining apparatus capable of preventing a generation of a root remaining portion to thereby provide high quality joined butted members.
Other objects and advantages of the present invention will be apparent from the following preferred embodiments.